Days of Thunder – April 1974 The Avengers #122

While the Avengers fight a group of terrorists known as the Zodiac on their spaceship, Thor accidentally throws his hammer into the void of space and reverts to Blake. Iron Man heads out into the void of space to retrieve it for his friend.

Iron Man grabs the hammer, which he is able to lift because it is zero gravity. Apparently, anyone can lift Mjolnir if it in the void of space. However, as he flies close enough to Earth’s gravity, the enchantment kicks in. Unable to resist, it pulls the Shellhead toward the Earth.

The hammer smashes into the Zodiac spaceship, now also falling back toward Earth, pinning Iron Man to the ship in the process. Fortunately, another Zodiac spaceship catches the first and Mjolnir comes to a rest within the artificial gravity created by the ship. Iron Man is freed and Thor is able to retrieve his hammer. The Avengers defeat Zodiac.